1. Field of the Invention
This invention concerns improvements to injection molds intended for the production of composite bodies such as multicolored light covers or components made of several different materials.
2. History of the Art
The injection molding process covered by the French additional certificate No. 2 425 317 is well known, and describes also the mold involved. This mold is fitted with cross blades which form the side walls of several cavities in alignment with each other and in which materials of different colors are injected. After completion of the injection phase, the blades are moved transversally so that the still empty cavity can be filled by a new injection, whereby the side walls are formed by the already molded elements.
It can be easily understood that when the parts to be produced are rather thick, the blades deflect under the injection pressure, so that they practically cannot be moved again. In such conditions, the mold described in the aforementioned French certificate cannot be used for the production of thick parts in several colors and/or materials.
We also know, as per document FR No. 2 462 261, a mold that can be used for the injection of thick composite parts thanks to an injection ram that comes and rests against the bottom of the cavity in order to form the side walls of two chambers in which materials of different colors and/or qualities are injected, either simultaneously or successively. The ram is then displaced so as to obtain between its end and the bottom of the cavity a third chamber in which another material is injected. It is easy to understand that the ram cannot be moved with a sufficient degree of accuracy to prevent any offset of the third injection with respect to the first two injections. Such an offset is absolutely inacceptable for certain parts, and consequently this type of mold cannnot be used in some applications.
We also know so-called "transfer molds" consisting of one ram and several dies, whereby successive injections are made through the ram, while the component under process is progressively transferred from one die to the next one, progressively to the last injection. It is easy to understand that such equipment is very expensive and that the elements molded in a given die can break when being transferred to the next die.
Lastly, in Japanese document 57-203 531 a mold is disclosed made of two blocks in each of which a partial cavity is bored, the form of which corresponds to that of one of the elements of the component to be produced. This element is obtained by a first injection in said cavity, while a sliding part is offset with respect to the middle plane of the cavity intended for the molding of at least one other element and which is positioned in a fixed part of the mold. The other element is injected after the sliding part has been returned to the position in which its cavity is level with an indent.